Slit illuminating device

ABSTRACT

A slit illuminating device having a plurality of linear surface mirrors, each partially surrounding a light source, whereby the illumination and the distribution of illumination at the slit section can be maintained uniform and stable, even when changes occur in the position of the light source.

This is a continuation-in-part of application Ser. No. 948,399, filedOct. 4, 1978, now abandoned.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to a slit illuminating device capable ofperforming uniform illumination of light at a slit section irrespectiveof the position of a light source.

2. Description of the Prior Art

There have so far been used generally reflecting mirrors having aquadratic surface such as ellipsoidal, parabolic, and hyperbolic mirrorswhen viewed in cross-section, or a simple linear surfaced mirror as thereflecting mirror for the slit illuminating device. For the linearsurfaced reflecting mirror, there can be enumerated such one as shown inFIG. 1 of this application, and one that consists of a plurality oflinear surfaced mirrors as shown in U.S. Pat. No. 3,777,135. In U.S.Pat. No. 3,777,135, divergent light from a light source is reflected byeach reflecting mirror, and this reflected light is used as thedivergent light for overall irradiation of an image original. Each ofthe linear surfaced mirrors takes such a position that its light pathlength may continuously decrease or increase relative to one end of theimage original to the other end thereof. However, it does not, at least,take a structure of the quadratic surface having light convergingproperty such as an ellipsoid. This constitutes a point of differencebetween the slit-exposure and the overall exposure. In other words,while the former is light-converging, the latter is light-diverging.This difference becomes evident in the presence or absence of the lightconverging property, when compared with a reflection factor of aconventional multi-surfaced mirror aimed at easiness in its manufacture.

In the case of the linear surfaced mirror as shown in FIG. 1, there issuch a disadvantage that overall loss in the quantity is great, sincelight beam from a light source is diverged, although relatively stabledistribution of illumination can be obtained at the slit section, evenwhen a light source position substantially deviates from that where itshould primarily be.

Also, as shown in FIG. 2, when the reflecting mirror has the quadraticsurface in its cross-section such as ellipsoidal, parabolic, andhyperbolic surfaces, there can be performed efficient light illuminationonce the light source is fixed at the first focus position, because thefocus can be determined strictly. On the contrary, when the light sourcedeviates from the particular position, there arises such a disadvantagethat the illumination and the distribution of illumination at the slitsection varies largely. In order to solve such disadvantage, laid-openJapanese Patent Application No. 51-23725 discloses a reflecting mirror,in which the quadratic surface mirror is slit into two portions, andsuch split reflecting mirrors are arranged with their focus positionsbeing differentiated. Such reflecting mirror, however, is complicated inits manufacture and adjustment of the focus position, since such doublefocus position requires adjustment in their inter-relationship.Moreover, there still remains such a question as to whether irregularityin the illumination can be reduced or not, even when the light sourceposition deviates in the direction perpendicular to the principal axis.

SUMMARY OF THE INVENTION

It is therefore an object of the present invention to provide a slitilluminating device capable of performing uniform and stable lightillumination at the slit section, even when there occurs substantialchanges in the position of the light source.

This object of the present invention can be attained by surrounding thelight source which extends in parallel with the longitudinal directionof the slit section, with a multi-linear surfaced mirror, thelongitudinal direction of which is in parallel with the light source.Here, the length in the short side direction of each linear surfacedmirror in the multi-surfaced mirror is determined by the fittingposition of the light source, positional relationship between the slitsection and the multi-surfaced mirror, and the size of the light source,and so on.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1A and 1B indicate cross-sectional view of a reflecting mirrorusing a conventional flat surface reflecting mirror;

FIG. 2A shows a cross-section of a reflecting mirror using aconventional ellipsoidal reflecting mirror, wherein the position of thelight source filament is at the focal point of the ellipsoid;

FIG. 2B also shows a cross-section of the ellipsoidal reflecting mirrorin FIG. 2A, wherein the light source filament is deviated from the focalposition;

FIG. 3 is a graphical representation showing variations in the lightquantity at a portion to be illuminated when the light source filamentin the abovementioned ellipsoidal reflecting mirror deviates from itsfocus;

FIG. 4 is an explanatory view showing a moving direction of the lightsource;

FIG. 5 is a cross-sectional view of a multi-linear surface reflectingmirror according to the present invention;

FIG. 6 is a graphical representation showing variations in the lightquantity due to positional deviation of the light source filament in themulti-linear surface reflecting mirror;

FIG. 7A is a cross-sectional view of an arrangement of anotherembodiment according to the present invention; and

FIG. 7B is a cross-sectional view of an arrangement of furtherembodiment according to the present invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

In the following, the present invention will be described in detail inreference to the accompanying drawing showing a preferred embodiment ofthe present invention.

FIGS. 1A and 1B indicate an illuminating condition of the slit sectionby the reflecting mirror utilizing a conventional linear surface mirror.In FIG. 1A showing an illuminating light path diagram in the case thelight source filament 3 of where the lamp 2 is at a position where theabovementioned reflecting mirror 1 should primarily be, the illuminatinglight quantity to a portion 4 to be illuminated, out of the lightquantity irradiated from the filament 3, is very slight. On the otherhand, as shown in FIG. 1B, the difference in the distribution ofillumination and the illumination at the portion 4 to be illuminated isvery small in comparison with a case of the abovementioned FIG. 1A, evenwhen the position of the light source filament 3 of the lamp 2 isdeviated from the primary position of the reflecting mirror 1. However,when the linear surface mirror is used as mentioned above, efficiency inuse of light from the light source remarkably lowers.

For the other type of the conventional reflecting mirror than theabovementioned linear surface mirror to reduce loss in the lightquantity, there are ellipsoidal, parabolic, hyperbolic, or otherquadratic surface reflecting mirrors.

FIGS. 2A and 2B illustrate an example of ellipsoidal reflecting mirrors6 and 7 split into two portions relative to the optical axis 5. As shownin FIG. 2A, when the light source filament 3 is at a position where itshould primarily be, i.e., at a focal position of each of theellipsoidal reflecting mirrors which have been split into two relativeto the optical axis 5, light emitted from the light source filament 3can be illuminated with high efficiency onto the portion 4 to beilluminated with relatively small loss in the light quantity. However,as shown in FIG. 2B, when the position of the light source filament 3 isdeviated from the position where it should primarily be, i.e., at aposition away from the common focal position of the respectiveellipsoidal reflecting mirrors 6 and 7 as divided into two relative tothe optical axis 5 (FIG. 2B, this shows a case where the light sourcefilament is positioned in the direction where it is away from theportion 4 to be illuminated along the optical axis 5), the light fromthe light source filament 3 does not sufficiently illuminate the portion4 to be illuminated, as the result of which illumination to the portion4 to be illuminated at a position where the light source filament shouldprimarily be, and the distribution of illumination as well as theillumination at the portion 4 to be illuminated vary remarkably.

FIG. 3 is a graphical representation showing variations in lightquantity at the portion 4 to be illuminated, when the light sourcefilament in the ellipsoidal reflecting mirror in FIG. 2A deviates from aposition where the light source filament should primarily be. In thisgraphical representation, a solid line 8 shows a quantity of deviationof the light source filament 3 on the optical axis 5 to be shown in FIG.4. A position O indicates a place where the light source filament 3should primarily be, and positive symbols indicate a direction a, alongwhich the filament 3 approaches the portion 4 to be illuminated (vide:FIG. 4). A dash line 9 in FIG. 3 indicates variations in the lightquantity at the abovementioned portion 4 to be illuminated, when thelight source filament upwardly deviates by 1 mm in the directionperpendicular to the optical axis 5, and varies in parallel with theoptical axis (b-b' in FIG. 4). Also, a dot-and-dash line 10 in FIG. 3shows variations in the illuminating light quantity at the portion 4 tobe illuminated, when the light source filament deviates opposite to thecase of the abovementioned dash line by 1 mm in the directionperpendicular to the optical axis 5, and varies in parallel with theoptical axis 5 (c-c' in FIG. 4). Incidentally, a negative symbol in FIG.3 denotes that the light source filament 3 is away from the portion 4 tobe illuminated, and symbols a', b' and c' indicate its direction andvariation.

As will be apparent from FIGS. 2 and 3, the deviation of the lightsource filament from the focal position of the ellipsoidal reflectingmirror brings about substantial changes in the light quantity at thelight source section, whereby the distribution of illumination at theportion 4 to be illuminated largely varies to influence the settingconditions of the image formation. The same thing can be said of areflecting mirror of a quadratic surface other than the ellipsoid.

FIG. 5 shows one embodiment of the present invention in itscross-section. The reflecting mirrors 11 and 12 in FIG. 5 serve to solvethe problem of shortage in the light quantity of the linear surfacemirror and the problem of variations in the distribution of illuminationdue to positional errors by the ellipsoidal reflecting mirror. Thereflecting mirror 11 is positioned near the slit section, while thereflecting mirror 12 is positioned away from the slit section. Theentire reflected light from the mirrors 11 and 12 effectively irradiatesthe slit section. As shown in FIG. 5, the reflecting mirrors 11 and 12having a configuration as split into two by the optical axis 5 andhaving different eccentricity in the case of, for example, anellipsoidal reflecting mirror, are composed of a plurality of continuouslinear surfaced reflecting mirrors. Each of the linear surfacedreflecting mirrors is disposed at a position, in a size and direction toreflect light from the light source filament to the portion 4 to beilluminated. Accordingly, those light beams from the light sourcefilament 3, corresponding in number to the linear surfaces which thereflecting mirrors 11 and 12 possess, illuminate the portion 4 to beilluminated, whereby sufficient light quantity can be obtained at thisportion 4. A reference numeral 19 designates a virtual image due to themulti-surfaced mirror within the permissible range 18 of the lightsource filament 3. By connecting the virtual image 19 and the slitsection 4, the position, size and direction of each of the linearsurfaced mirrors constituting the multi-surfaced reflecting mirror canbe determined. Dotted regions 13 are the extension from each of thelinear surfaced mirror and the slit section as connected. A referencenumeral 14 designates a virtual image of the light source filament 3 tobe formed by the multi-surfaced mirror whem the filament 3 is at theideal position.

FIG. 6 is a graphical representation showing the distribution ofillumination when the light source filament is deviated from a positionwhere it should primarily be. In the graphical representation, a solidline 15 denotes a distribution of illumination due to movement of thelight source filament on the optical axis, and a dash line 16 denotes adistribution of illumination when the light source filament is deviatedby 1 mm in the same direction b-b' as in the case of changing thedirection of the light source filament shown in FIG. 4, and then movedin parallel with the optical axis 5. A dot-and-dash line 17 denotes adistribution of illumination when the light source filament is deviatedby 1 mm in the same direction as the direction c-c' in FIG. 4, and thenmoved in parallel with the optical axis. Accordingly, the reflectingmirror in the present invention can illuminate the portion 4 to beilluminated with a sufficient light quantity, and perform stableillumination free from fluctuation in the distribution of illuminationat the portion 4 to be illuminated, even when the light source filamentis deviated more or less from the position where it should primarily be,i.e., if it is within a permissible range 18.

FIGS. 7A and 7B show other embodiment. In each of the arrangements shownin these Figures, the mirror 11 is more inclined in the clockwisedirection with respect to the lamp 2 than in the foregoing embodiment,so that the light reflected by the mirror is substantially parallel withthe slit portion 4. The light is then reflected by the third mirror, aplane mirror 21 (FIG. 7A) or a mirror having a quadratic surface (FIG.7B) to illuminate the slit portion 4, while the light reflected by themirror 12 directly illuminates the slit portion 4. It will be understoodfrom FIGS. 7A and 7B that the light from the mirror 11 and the lightfrom the mirror 12 are incident to the slit portion 4 substantiallysymmetrically. Except for those described above in this paragraph, thearrangement is the same as of the embodiment described hereinbefore.

The reflecting mirror according to the present invention is only forslit illumination. However, it is also applicable to a case where animage original placing or support table is fixed and the light sourceand the reflecting mirror move, and to a case where the image originalplacing table moves and the light source and the reflecting mirror arefixed.

As stated in the foregoing, the present invention aims at removingirregularity in illumination due to errors in its manufacture andfitting so as to constantly obtain stable illumination. For thispurpose, the quadratic surface mirror of good illuminating efficiency isused in an illuminating device having a plurality of linear surfacedmirrors, each being relatively close to the quadratic surface.

What we claim is:
 1. A slit illuminating device for an imagereproduction apparatus, which comprises:(a) an original support tablehaving a slit portion for slit illumination of an original; (b) atubular shaped light source arranged with its longitudinal axis spaced apredetermined distance from and parallel to a reference line whichextends along the length of said slit; and (c) a multi-surfaced mirrorpartially surrounding said light source and comprising a plurality ofplanar mirrors provided on both sides of a plane defined by thelongitudinal axis of said light source and the reference line, whereinthe respective length of each planar mirror, when viewed incross-section defined by a plane perpendicular to the reference line, issuch that it transmits an effective bundle of light, as if emitted froma corresponding enlarged virtual image of said light source, to saidslit portion, the size of the enlarged image being determined inaccordance with an acceptable deviation of said light source from apredetermined mounting position.
 2. A slit illuminating device for animage reproduction apparatus, which comprises:(a) an original supporttable having a slit portion for slit illumination of an original; (b) atubular shaped light source arranged with its longitudinal axis spaced apredetermined distance from and parallel to a reference line whichextends along the length of said slit; (c) a first multi-surfaced mirrorcomprising a plurality of planar mirrors located above a plane definedby the longitudinal axis of said light source and the reference line ofsaid slit portion, wherein the respective length of each planar mirror,when viewed in cross-section defined by a plane perpendicular to thereference line, is such that it transmits an effective bundle of light,as if emitted from a corresponding enlarged virtual image of said lightsource, in a direction substantially parallel to the support table; (d)a second multi-surfaced mirror comprising a plurality of planar mirrorslocated below said plane defined by the longitudinal axis and referenceline, wherein the respective length of each said planar mirrors whenviewed in cross-section defined by a plane perpendicular to thereference line, is such that it transmits an effective bundle of light,as if emitted from a corresponding enlarged virtual image of said lightsource, to said slit portion; and (e) a third mirror for receiving thelight reflected by said first multi-surfaced mirror and directing thatlight to incident the slit section so as to substantially completelyoverlap the light incident thereon from the second multi-surfacedmirror; wherein the size of the enlarged images for the respectiveplanar mirrors of said first and second multi-surfaced mirrors isdetermined in accordance with an acceptable deviation of said lightsource from a predetermined mounting position.
 3. A device according toclaim 1 or 2, wherein said planar mirrors are arranged along a quadraticsurface.